Typically, the endless belt of a conveyor is driven either by an end drive unit positioned to drive a spindle or roller located at either end of a conveyor frame, or by a center drive unit positioned along the length of the conveyor frame and mounted beneath the conveyor frame. In a center drive unit, the continuous belt is wound through a series of rollers, including a drive roller and a tensioning roller, to impart the required force to the conveyor belt. One such center drive unit is illustrated in Ewert U.S. Pat. No. 5,203,447, the disclosure which is hereby incorporated by reference. As can be understood in the Ewert patent, the endless belt is entrained around six separate rollers (two drive rollers, two idler rollers and two belt tensioning rollers) positioned in a tortured path beneath the conveyor frame. The tortured path increases the driven traction on them belt due to the belt tension and the degree of wrap of the belt around the drive rollers.
Although the center drive unit illustrated in the '447 patent is efficient for driving the conveyor belt, threading the conveyor belt through the center drive unit is a tedious and time consuming task. Further, the multiple rollers require additional parts and manufacturing costs, such as for machining of the outer walls of the various rollers.
An attempt to improve upon the design of the center drive unit is described in pending U.S. patent application Ser. No. 10/385,906 filed March 11, 2003, the disclosure of which is herein incorporated by reference. In this construction, the conveyor belt is passed over a single guide roller, beneath a single drive roller and over a single tensioning roller. Such a design minimizes the number of components and provides a compact system that can easily be threaded with the conveyor belt to obtain a sufficient degree of belt wrap for achieving belt traction.
While this center drive unit is a significant advance over the Ewert arrangement, it is still necessary to machine the peripheral surface of the drive roller to acquire the smooth surface for proper engagement with the belt. Because some drive rollers may be four feet in length and six inches in diameter, such machining can be labor intensive and costly. It also remains necessary to machine the outer wall of the drive roller to form a circumferential groove for receiving a centrally located rib on the belt used to prevent lateral movement or skewing of the belt on the conveyor.